Ultrasound imaging is a medical imaging technique for imaging organs and soft tissues in a human body. Ultrasound imaging uses real time, non-invasive high frequency sound waves to produce a two-dimensional (2D) image and/or a three-dimensional (3D) image.
Ultrasound imaging system operators often rely upon technology when performing a medical procedure, such as a biopsy procedure. A tracking system may provide positioning information for the needle with respect to the patient, a reference coordinate system, or the ultrasound probe, for example. An operator may refer to the tracking system to ascertain the position of the needle even when the needle is not within the region or volume of tissue currently being imaged and displayed. As such, the tracking or navigation system allows the operator to visualize the patient's anatomy and better track the position and orientation of the needle. The operator may use the tracking system to determine when the needle is positioned in a desired location such that the operator may locate and operate on a desired or injured area while avoiding other structures. Increased precision in locating medical instruments within a patient may provide for a less invasive medical procedure by facilitating improved control over smaller instruments having less impact on the patient. Improved control and precision with smaller, more refined instruments may also reduce risks associated with more invasive procedures such as open surgery.
Tracking systems may be electromagnetic or optical tracking systems, for example. Electromagnetic tracking systems may employ a permanent magnet as an emitter and a sensor as a receiver, or can employ coils as receivers and transmitters. Magnetic fields generated by the permanent magnet(s) or transmitter coil(s) may be detected by the sensor(s) or receiver coil(s) and used to determine position and orientation information of a surgical instrument, for example. Prior to performing a medical procedure, the tracking system is calibrated. For example, in a tracking system comprising a permanent magnet emitter coupled to or within a surgical needle and one or more sensors coupled to or within a probe, the needle may be removed from the surgical environment so that the tracking system can be calibrated while the probe is held stationary to remove or zero-out ambient magnetic fields detected by the sensor(s). However, even a slight subsequent movement (e.g., a tilt or a rotation relative to the calibration position or orientation) of the hand-held ultrasound probe during a procedure can cause positioning errors in the tracking system, which may necessitate recalibration of the tracking system. In known tracking systems that use permanent magnets, for example, recalibration is typically performed by removing the surgical instrument that includes the emitter from the surgical environment, which could be inconvenient when the surgical instrument is within a patient, for example, and then holding the probe stationary during recalibration.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.